The present invention relates generally to the field of electrical rotating machines, such as motors, generators, or the like. More particularly, the present techniques concern the electrical/electromechanical performance of rotor assemblies of such rotating machines.
Electrical rotating machines, such as electric motors, generators, and other similar devices, are quite common and may be found in diverse industrial, commercial, and consumer settings. These machines are produced in a variety of mechanical and electrical configurations. The configuration of these devices may depend upon the intended application, the operating environment, the available power source, or other similar factors. In general, these devices include a rotor surrounded at least partially by a stator.
For instance, one common design of electrical rotating machine is the induction motor, which is used in numerous and diverse applications. In industry, such motors are employed to drive various kinds of machinery, such as pumps, conveyors, compressors, fans and so forth, to mention only a few. Conventional alternating current (AC) electric induction motors may be constructed for single-phase or multiple-phase power.
Induction motors typically employ a rotor assembly positioned within a stator assembly that includes a slotted core in which groups of coil windings are installed. More particularly, the rotor assemblies of such motors often include a core formed of a series of magnetically conductive laminations arranged to form a lamination stack capped at each end by electrically conductive end rings. Additionally, typical rotors include a series of conductors that are formed of a nonmagnetic, electrically conductive material and that extend through the rotor core. These conductors are electrically connected to one another via the end rings, thereby forming one or more closed electrical pathways. For example, the conductors may include a plurality of rotor bars extending axially through the series of magnetically conductive laminations and arranged at different angular positions around the axis of the rotor.
In squirrel cage induction motors, the rotor bars and end rings are typically formed by a casting process in which the rotor is placed in a mold and a molten metal is poured into the rotor slots to form the rotor bars and end rings. Flaws in the rotor can result in undesirable reduction in the electrical/electromechanical performance, e.g., reduced efficiency, excessive slip under load, unexpected torque pulsations, and higher than expected operating temperatures. It is not possible to visually inspect the quality of the resultant casting because the resultant rotor bars are embedded within the rotor. To check for the presence of voids and contaminants in the casting, it has typically been necessary to cut open a representative or suspect rotor, essentially destroying the rotor. Similarly, the electrical characteristics of rotors formed by other manufacturing techniques generally cannot be tested without destroying the rotor.